Note: Descriptions are shown in the official language in which they were submitted.
CA 02716832 2012-12-24
HEAT REMOVAL SYSTEM AND METHOD FOR LIGHT EMITTING DIODE
LIGHTING APPARATUS
CLAIM OF PRIORITY
[0001] This application claims priority to U.S. Provisional Patent
Application No.
61/032,988 entitled "THERMAL CONVECTION MODEL FOR LED LAMPS," which
was filed on 2 March 2008, and to U.S. Patent Application No. 12/370,521
entitled
"HEAT REMOVAL SYSTEM AND METHOD FOR LIGHT EMITTING DIODE
LIGHTING APPARATUS," which was filed on 12 February 2009.
BACKGROUND
[0002] A light-emitting diode (LED) is a semiconductor diode that emits
incoherent narrow-spectrum light when electrically biased in the forward
direction of
the p-n junction. LEDs have unique advantages over other lighting solutions.
They
operate at a high efficiency to produce more light output with lower input
power, and
have an inherently longer service life. For example, LEDs typically produce
more light
per watt than incandescent bulbs, and last much longer. Also, the output light
of LEDs
can be color matched and tuned to meet stringent lighting application
requirements. In
contrast, the output light of incandescent bulbs and fluorescent lights can
not be as
effectively tuned. Thus, LEDs which are often used in battery powered or
energy
saving devices are becoming increasingly popular in higher power applications
such
as, for example, flashlights, area lighting, and regular household light
sources.
[0003] Unlike incandescent bulbs and fluorescent lights, LEDs are
semiconductor devices that conventionally must operate at lower temperatures.
This is
so because, in part, the LED p-n junction temperature needs to be kept low
enough to
prevent degradation and failure. While incandescent bulbs and fluorescent
lights lose
heat by direct radiation from a very hot filament or gas discharge tube,
respectively,
LEDs must remove heat by conduction from the p-n junction to the case of the
LED
package before being dissipated. Conventional LED packages thus typically
employ
various heat removal schemes. The effectiveness of the heat removal scheme
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determines how well such LEDs perform, as cooler running temperatures yield
higher efficacy for a given level of light output.
[0004] One conventional passive approach to cooling LEDs provides a finned
heat
sink exposed to external air. In such an approach, the thermal choke point in
the
heat transfer equation is typically the heat sink to air interface. To
maximize heat
transfer across this interface, the exposed heat sink surface area is
typically
maximized, and the heat sink fins are typically oriented to take advantage of
any
existing air flow over the fins. Unfortunately, such a conventional passive
approach
does not effectively cool LEDs for various reasons. Thus, in typical LED
lighting
applications that utilize this approach, the LEDs are often operated at less
than half
of their available light output capacity, to extend their lifetime and to
preserve their
efficiency.
[0005] Other LED lighting applications utilize a conventional active approach
to
cooling LEDs that forces air over a finned heat sink with, for example, a
powered fan.
Another example is a patent pending product, referred to as "SynJet," which
uses a
diaphragm displacement method to "puff' air over a finned heat sink. While
such
active approaches may be more effective in removing heat from LEDs, they have
many negative issues. For example, these approaches typically utilized powered
components which add cost to a given LED lighting application. In addition,
these
approaches typically are noisy, typically exhibit parasitic electrical loss,
and typically
introduce unreliable moving parts.
[0006] The foregoing examples of the related art and limitations related
therewith
are intended to be illustrative and not exclusive. Other limitations of the
related art
will become apparent upon a reading of the specification and a study of the
drawings.
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SUMMARY
[0007] A heat removal assembly for a light emitting diode lighting apparatus
is
.described. One embodiment of the heat removal assembly includes a plurality
of
fins configured to receive heat from a light emitting diode. In the plurality
of fins, two
adjacent fins are separated by a gap width, and each fin has a fin length. The
heat
removal assembly also includes a duct configured to draw a stack-effect
airflow
through the plurality of fins to remove heat from the plurality of fins. The
gap width
separating two adjacent fins and the fin length of each of the fins are
configured to
prevent boundary layer choking the plurality of fins. In one embodiment, the
heat
removal assembly also includes a conductor and a thermal storage system
configured to receive heat from the light emitting diode. A lighting apparatus
including the heat removal assembly, a light emitting diode, and a connector
plug is
also described. In one embodiment, the lighting apparatus can be installed in
a
recessed can in which incoming and outgoing flows of a stack-effect airflow
are
separated. Methods for removing heat from a light emitting diode are also
described.
[0008] This Summary is provided to introduce a selection of concepts in a
simplified form that are further described below in the Detailed Description.
This
Summary is not intended to identify key features or essential features of the
claimed
subject matter, nor is it intended to be used to limit the scope of the
claimed subject
matter.
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BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Fig. 1 depicts a block diagram of a lighting apparatus including a heat
removal assembly according to an embodiment of the invention.
[00010] Fig. 2 depicts a block diagram of a lighting apparatus including a
heat
removal assembly according to an embodiment of the invention.
[00011] Fig. 3a depicts a block diagram of a lighting apparatus including a
heat
removal assembly according to an embodiment of the invention.
[00012] Fig. 3b depicts a block diagram of a lighting apparatus including a
heat
removal assembly according to an embodiment of the invention.
[00013] Fig. 3c depicts a block diagram of a lighting apparatus including a
heat
removal assembly according to an embodiment of the invention.
[00014] Fig. 4 depicts an installation including a lighting apparatus
according to an
embodiment of the invention.
[00015] Fig. 5 depicts a flowchart for performing a method of removing heat
from a
light emitting diode according to an embodiment of the invention.
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DETAILED DESCRIPTION
[00016] Described in detail below are heat removal systems and methods for a
light
emitting diode lighting apparatus.
[00017] Various aspects of the invention will now be described. The following
description provides specific details for a thorough understanding and
enabling
description of these examples. One skilled in the art will understand,
however, that
the invention may be practiced without many of these details. Additionally,
some
well-known structures or functions may not be shown or described in detail, so
as to
avoid unnecessarily obscuring the relevant description. Although the diagrams
depict components as functionally separate, such depiction is merely for
illustrative
purposes. It will be apparent to those skilled in the art that the components
portrayed
in this figure may be arbitrarily combined or divided into separate
components.
[00018] The terminology used in the description presented below is intended to
be
interpreted in its broadest reasonable manner, even though it is being used in
conjunction with a detailed description of certain specific examples of the
invention.
Certain terms may even be emphasized below; however, any terminology intended
to be interpreted in any restricted manner will be overtly and specifically
defined as
such in this Detailed Description section.
[00019] Fig. 1 depicts a block diagram of lighting apparatus 100 according to
one
embodiment of the invention. In the example of Fig. 1, lighting apparatus 100
includes duct 110, fin assembly 120, conductor 130, and light emitting diode
("LED")
140. Duct 110, fin assembly 120, and conductor 130 comprise a heat removal
assembly of lighting apparatus 100. As discussed below, heat generated by LED
140 during operation is transferred by conduction through conductor 130 to fin
assembly 120, and then transferred by convection to stack-effect airflow 112
flowing
through fin assembly 120 and duct 110.
[00020] In various embodiments of the invention, LED 140 includes one LED or a
plurality of LEDs. In embodiments wherein LED 140 includes a plurality of
LEDs, the
LEDs may be configured to emit light of a single color or of a uniform
spectrum, or
alternatively several of the LEDs may be configured to emit light of varying
colors, or
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having different spectrums. In various embodiments wherein LED 140 includes a
plurality of LEDs, the LEDs may be configured to emit light in one direction
or in
several directions. In further various embodiments wherein LED 140 includes a
plurality of LEDs, the LEDs may be electrically coupled in series, in
parallel, or in
various combinations of both. Although in this discussion LED 140 is referred
to as
including at least one light emitting diode, various embodiments of the
invention may
include a light emitting device other than a light emitting diode. LED 140 may
be
configured to emit light through a lens or other optical structure.
[00021] In one embodiment of the invention, LED 140 is coupled to conductor
130
to transfer heat generated by LED 140 during operation (e.g., while LED 140 is
receiving power and emitting light) to conductor 130 by conduction. To
facilitate
such conduction, LED 140 is coupled to conductor 130 utilizing, for example,
thermal
pads. A light emitting diode of LED 140 may transfer heat from an internal p-n
junction to the thermal pads according to a manufacturer-specified thermal
conductivity. In one embodiment of the invention, LED 140 is electrically
coupled to
a printed circuit board ("PCB") having an LED driver circuit for providing
power to
LED 140.
[00022] In one embodiment of the invention, conductor 130 has a mounting
surface
for LED 140 suited for efficient layout of a plurality of LEDs in LED 140. For
example, conductor 130 has, in one embodiment, an H-shaped top suited for an
efficient layout of a plurality of LEDs. In other embodiments conductor 130
may
utilize a differently shaped mounting surface. In various embodiments,
conductor
130 may be implemented with one type of material or multiple types of
materials.
For example, in one embodiment conductor 130 may be implemented as a copper
conductor. In another embodiment, for example, conductor 130 may be
implemented as a copper and aluminum conductor, wherein a copper subassembly
of conductor 130 is soldered, screwed, or otherwise coupled to an aluminum
subassembly. Although depicted with a square cross section in Fig. 1,
conductor
130 may be implemented in a variety of shapes and sizes.
[00023] Fin assembly 120 is configured to receive heat generated by LED 140
during operation from conductor 130, and is further configured to transfer the
heat by
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convection to stack-effect airflow 112 flowing through fin assembly 120 and
duct 110.
In various embodiments, in some cases like conductor 130, fin assembly 120 may
be
implemented with one type of material or multiple types of materials. For
example, in
one embodiment fin assembly 120 may be implemented as an aluminum fin
assembly. Although fin assembly 120 is depicted in Fig. 1 disposed to the left
of
conductor 130, fin assembly 120 may be disposed spatially with respect to
conductor
130 in a variety of ways according to the invention.
[00024] In one embodiment, conductor 130 and fin assembly 120 are
substantially
isothermal during operation of LED 140, because of a high thermal conductivity
of
conductor 130 and fin assembly 120 relative to a low thermal conductivity
between
fin assembly 120 and stack-effect airflow 112. Thus, in one embodiment
conductor
130 and fin assembly 120 have a substantially uniform operational temperature.
In
another embodiment, a temperature gradient exists across conductor 130 and fin
assembly 120, which together have an average operational temperature.
[00025] Exemplary fin 122 and exemplary fin 124 (collectively "fins 122 and
124") of
fin assembly 120 are shown in Fig. 1. Fins 122 and 124 are illustrative, and
in
various embodiments of the invention fin assembly 120 has more than two fins.
Further, although fins 122 and 124 are depicted as having diamond cross-
sections in
Fig. 1, various embodiments of the invention may implement a plurality of fins
of fin
assembly 120 as having, for example, rectangular cross sections, curved cross
sections, aerodynamically-improved cross sections, or other cross sections.
Further
still, although fins 122 and 124 are depicted as discrete fins in Fig. 1, in
other
embodiments of the invention fin assembly 120 comprises an "overlapping"
plurality
of fins having a more-complex geometry. For example, in various embodiments,
fin
assembly 120 may comprise a plurality of fins having a grid or hexagonal cross
section across a plane perpendicular to stack-effect airflow 112 (i.e., a grid
or
hexagonal cross section as viewed from below lighting apparatus 100 looking in
the
direction of stack-effect airflow 112).
[00026] As shown in Fig. 1, fins 122 and 124 each have a fin width and a fin
length
(or "chord length"), and fins 122 and 124 are separated by a gap width. Fins
122
and 124 each also have a fin depth not depicted in Fig. 1. In some
embodiments,
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each fin in fin assembly 120 has a uniform fin length, fin width, and fin
depth, while in
other embodiments several fins may have varying fin lengths, fin widths, or
fin
depths. Also, in some embodiments each adjacent pair of fins in fin assembly
120
may have uniform gap widths, while in other embodiments various adjacent pairs
of
fins may have varying gap widths. Notably, in embodiments of the invention
wherein
fin assembly 120 comprises a plurality of fins having a grid or hexagonal
cross
section, the plurality of fins may still be characterized by a fin width, a
fin length, a fin
depth, and a gap width. Certain unique configurations of fin length, fin
width, fin
depth, and gap width enable the heat removal assembly of lighting apparatus
100 to
achieve improved heat removal performance according to the invention, as
discussed further below.
[00027] Duct 110 is configured as a passage for stack-effect airflow 112,
which
flows through both fin assembly 120 and duct 110, and which carries heat away
from
fin assembly 120 by convection. Duct 110, which has a duct length, is
configured
with respect to fin assembly 120 to exploit a "stack effect" (also called a
"heatalator"
or "chimney effect"). In particular, ambient air, preferably cooler than an
operational
temperature of fin assembly 120 described above, is heated by contact or
proximity
to fin assembly 120. The heated air then buoyantly rises through fin assembly
120,
increasing in temperature as it remains in contact with or proximate to fin
assembly
120, causing a contemporaneous decrease in air density. A stack effect
provided by
duct 110 results in a greater buoyant force and hence greater air flow through
fin
assembly 120. Stack-effect airflow 112 is the resulting flow through fin
assembly
120 and duct 110. Notably, although stack-effect airflow 112 is depicted as a
line
between fins 122 and 124 and through duct 110, it is understood that stack-
effect
airflow 112 is, in one embodiment, a flow of air through substantially the
volume
unoccupied by the plurality of fins of fin assembly 120 and through
substantially the
volume of duct 110. Certain unique configurations of duct length of duct 112
enable
the heat removal assembly of lighting apparatus 100 to achieve improved heat
removal performance according to the invention.
[00028] The plurality of fins of fin assembly 120 impede stack-effect airflow
112
flowing through fin assembly 120 by, for example, reducing the inlet cross
section of
fin assembly 120. In an extreme case, wherein the sum of the fin widths of the
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plurality of fins equals the assembly width of fin assembly 120, stack-effect
airflow
112 is completely blocked. This is true both for a greater quantity of fins
having
relatively lesser fin widths, and for a lesser quantity of fins having
relatively greater
fin widths. Thus, to avoid blocking or impeding stack-effect airflow 112, the
number
of fins and the fin width of each fin should be reduced. However, the amount
of heat
transferred from fin assembly 120 to stack-effect airflow 112 is substantially
proportional to the total surface area of the plurality of fins of fin
assembly 120. The
total surface area of the plurality of fins is substantially dependent on, in
one
embodiment, the fin length and fin depth of each fin. Thus, to increase the
amount
of heat transferred from fin assembly 120 to stack-effect airflow 112, for a
given fin
length, fin depth, and fin width the number of fins should be increased.
[00029] According to the invention, a balance is struck by fin assembly 120
between the alternate rationales for decreasing and increasing the number of
fins
stated above. Informing the balance is the novel recognition that the number
of fins
of fin assembly 120 may be increased without unduly impeding stack-effect
airflow
112, thereby improving the amount of heat transferred from fin assembly 120 to
stack-effect airflow 112, until boundary layers of each fin begin interfering
in the
volume between each adjacent pair of fins. If the number of fins is increased
further,
and the gap width is thereby decreased below a critical distance, interference
between the boundary layers of the fins "chokes" stack-effect airflow 112
along the
fins, thereby detrimentally impeding stack-effect airflow 112. Notably, for a
given
assembly width and fin width, the number of fins required to choke stack-
effect
airflow 112 is less than the number of fins required to completely block stack-
effect
airflow 112, because the boundary layer width of each fin is wider than the
fin width
of each fin. Thus, the gap width separating two adjacent fins is configured to
be
greater than the boundary layer widths of the two adjacent fins.
[00030] In addition to the unique balance struck regarding the number of fins
of fin
assembly 120, a balance is struck, in various embodiments, in the ratio of the
duct
length of duct 110 to the fin length of fin assembly 120. Were duct 110 and
fin
assembly 120 configured in a conventional manner, the ratio might be very low,
such
that the fin length of fin assembly 120 is nonzero and the duct length is
substantially
zero. In effect, a conventional configuration might maximize the fin length
and
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minimize the duct length, or forgo utilizing duct 110 at all. At first glance,
such a
configuration has the apparent advantage of increased total surface area of
the
plurality of fins, for a given fin depth of each fin, and also of increased
mass. While
increasing the mass of fin assembly 120 would marginally improve the
performance
of fin assembly 120 as a heat sink, such a configuration would ultimately be
ineffective because the total thermal capacity of conductor 130 and fin
assembly 120
would not be significantly improved by adding mass through fin length
lengthening,
and further because fin length lengthening ultimately reintroduces boundary
layer
interference issues along the plurality of fins. In contrast with such a
conventional
configuration, various embodiments of the invention utilize novel higher
ratios of duct
length to fin length. For example, in various embodiments the duct length may
be
equal to or slightly longer than the fin length. For another example, in
various
embodiments the duct length may be five to ten times the fin length. By so
configuring such embodiments, boundary layer interference issues are avoided,
and
the flow of stack-effect airflow 112 through fin assembly 120 and duct 110 is
greatly
improved.
[00031] Fig. 2 depicts a block diagram of lighting apparatus 200 according to
one
embodiment of the invention. In the example of Fig. 2, lighting apparatus 200
includes duct 110, fin assembly 120, conductor 130, and light emitting diode
("LED")
140 of lighting apparatus 100. As discussed above regarding lighting apparatus
100,
heat generated by LED 140 during operation is transferred by conduction
through
conductor 130 to fin assembly 120, and then transferred by convection to stack-
effect airflow 112 flowing through fin assembly 120 and duct 110. Thus, duct
110, fin
assembly 120, conductor 130, and light emitting diode ("LED") 140 of lighting
apparatus 200 substantially correspond to those of lighting apparatus 100,
except in
variations noted below.
[00032] Lighting apparatus 200 additionally includes thermal storage system
250.
Duct 110, fin assembly 120, conductor 130, and thermal storage system 250
comprise a heat removal assembly of lighting apparatus 200. Thermal storage
system 250 corresponds, in one embodiment of the present invention, to a
thermal
storage system as described in U.S. Patent Application No. 12/237,313 entitled
"THERMAL STORAGE SYSTEM USING PHASE CHANGE MATERIALS IN LED
CA 02716832 2012-12-24
LAMPS," which was filed on September 24, 2008, by Matthew Weaver et al. In one
embodiment, a phase change material (PCM) included in thermal storage system
250 is used to absorb heat received via conduction from conductor 130 during
operation of LED 140. The unique configuration of lighting apparatus 200,
which has
thermal storage system 250 and also has the heat removal assembly of lighting
apparatus 100, enables the heat removal assembly of lighting apparatus 200 to
achieve improved heat removal performance according to the invention.
[00033] In the example of Fig. 2, thermal storage system 250 is depicted
with a
rectangular cross section, but in various embodiments thermal storage system
250
may be implemented in a variety of shapes and sizes. Fig. 2 further depicts
thermal
storage system 250 coupled to duct 110 across surface 252. In some embodiments
of the invention, surface 252 is a thermally insulating surface such that
thermal
storage system 250 and duct 110 do not thermally interact. In such
embodiments, the
heat characteristics of stack-effect airflow 112 and of thermal storage system
250 are
substantially independent. In other embodiments, surface 252 is instead a
thermally
conducting surface, such as, for example, a surface implemented with material
utilized in conductor 130. In such other embodiments, thermal storage system
250
and duct 110 may thermally interact, such that heat is transferred from stack-
effect
airflow 112 to thermal storage system 250, or vice versa. Notably, in some
embodiments not depicted in Fig. 2, thermal storage system 250 and duct 110
are
not coupled across surface 252 but are instead physically distinct and
separated by,
for example, air, a vacuum, or other portions of lighting apparatus 200.
[00034] In several embodiments, thermal storage system 250 and fin assembly
120 are both configured to receive heat from LED 140 via conductor 130. In
such
embodiments, the proportion of the heat generated by LED 140 that is conducted
to
thermal storage system 250 instead of to fin assembly 120 may vary, for
example,
with changes in the ambient air temperature, with the passage of time during
operation as thermal storage system 250 stores heat energy, or with the
passage of
time after operation as thermal storage system 250 releases heat energy. In
one
embodiment, after operation of LED 140 has stopped, thermal storage system 250
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releases heat into fin assembly 120 via conductor 130, thereby maintaining
stack-
effect airflow 112 after operation.
[00035] A method for removing heat from LED 140 can be described with respect
to
Fig. 2. The method comprises providing thermal storage system 250, providing a
plurality of fins in fin assembly 120, and providing duct 110. The method
further
comprises configuring duct 110 to draw stack-effect airflow 112 through the
plurality
of fins, configuring a gap width separating two adjacent fins of the plurality
of fins to
reduce boundary layer choking along the plurality of fins, configuring a fin
length of
each of the plurality of fins to reduce boundary layer choking along the
plurality of
fins, and configuring a duct length of duct 110 to reduce boundary layer
choking
along the plurality of fins. The method also comprises operating LED 140,
conducting heat from LED 140 to the plurality of fins, conducting heat from
LED 140
to the thermal storage system, and convecting heat from the plurality of fins
to stack-
effect airflow 112. This method is depicted in flowchart 500 in Fig. 5.
[00036] Fig. 3a and Fig. 3b (collectively "Figs. 3a and 3b") depict a block
diagram of
lighting apparatus 300 according to one embodiment of the invention. Fig. 3a
depicts a side view of lighting apparatus 300, and Fig. 3b depicts a bottom
view of
lighting apparatus 300. In the example of Figs. 3a and 3b, lighting apparatus
300
includes duct 310, fin assembly 320, conductor 330, light emitting diode
("LED") 340,
thermal storage system 350, and printed circuit board ("PCB") 360. Duct 310,
fin
assembly 320, conductor 330, and thermal storage system 350 comprise a heat
removal assembly of lighting apparatus 300. In some embodiments of the
invention,
duct 310, fin assembly 320, conductor 330, LED 340, and thermal storage system
350 substantially correspond to duct 110, fin assembly 120, conductor 130, LED
140, and thermal storage system 250 of lighting apparatus 200, except in
variations
noted below. Thus, as discussed above regarding lighting apparatus 200, in
some
embodiments of the invention a portion of the heat generated by LED 340 during
operation is transferred by conduction through conductor 330 to fin assembly
320,
and then transferred by convection to stack-effect airflow 312 flowing through
fin
assembly 320 and duct 310, and another portion of the heat is transferred by
conduction through conductor 330 and fin assembly 320 to thermal storage
system
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350. In one embodiment of the invention, lighting apparatus 300 may omit
thermal
storage system 350.
[00037] As depicted in Figs. 3a and 3b, fin assembly 320 and duct 310 at least
partially enclose a volume that is substantially occupied by other
subassemblies of
lighting apparatus 300. Although depicted in Fig. 3b as having circular cross
sections, fin assembly 320 and duct 310 may have various other cross sectional
shapes in other embodiments of the invention. For example, in other
embodiments,
fin assembly 320 and duct 310 may have ellipsoidal, triangular, rectangular,
or yet
other cross sectional shapes. Thermal storage system 350 and conductor 330 may
have, in various embodiments, similarly varying cross sections. In one
embodiment
not depicted in Figs. 3a and 3b, fin assembly 320 and duct 310 are configured
to
pass through an interior volume of either or both of thermal storage system
350 and
conductor 330. In another embodiment not depicted in Figs. 3a and 3b,
conductor
330 is configured to pass through an interior volume of fin assembly 320 to
contact
thermal storage system 350.
[00038] As depicted in Figs. 3a and 3b, in one embodiment LED 340 is coupled
to
mounting surface 332 of conductor 330. To transfer heat generated by LED 340
during operation to conductor 330, LED 340 is coupled to mounting surface 332
utilizing, for example, thermal pads. In one embodiment of the invention,
mounting
surface 332 is suited for efficient layout of a plurality of LEDs in LED 340.
Mounting
surface 332 may be configured with, for example, a circular or semi-circular
top
suited for an efficient layout of a plurality of LEDs. In other embodiments,
mounting
surface 332 may utilize a differently shaped top, such as, for example, an H-
shaped
top or a rectangular top. In such embodiments, for example, mounting surface
332
may comprise multiple surfaces at different heights for mounting LED 340 and
PCB
360 at different heights.
[00039] As shown in Figs. 3a and 3b, conductor 330 may be mounted at a center
of
fin assembly 320. In various embodiments, conductor 330 may be implemented
with
one type of material or multiple types of materials. For example, in one
embodiment
conductor 330 may be implemented as a copper conductor. In another embodiment,
a portion of conductor 330 may be implemented as an aluminum conductor.
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Conductor 330 may be, for example, soldered, screwed, or otherwise coupled to
fin
assembly 320. Conductor 330 may be implemented in a variety of shapes and
sizes.
[00040] In one embodiment of the invention, LED 340 is electrically coupled
to
PCB 360. As shown in Figs. 3a and 3b, PCB 360 may be configured to fit within
a
circumference of fin assembly 320. As further shown in Figs. 3a and 3b, PCB
360
may be configured to be coupled to mounting surface 332 of conductor 330
adjacent
to LED 340. By so configuring PCB 360, lighting apparatus 300 advantageously
achieves, for example, a compact form that efficiently utilizes space.
Although PCB
360 is depicted as having a rectangular cross section in Fig. 3b, in another
embodiment PCB 360 may have, for example, a circular cross section or another
cross section. PCB 360 includes, in one embodiment, an LED driver circuit for
providing power to LED 140. The LED driver circuit corresponds, in one
embodiment,
to a driver circuit as described in U.S. Patent No. 7,986,107 entitled
"ELECTRICAL
CIRCUIT FOR DRIVING LEDS IN DISSIMILAR COLOR STRING LENGTHS," by
Matthew Weaver.
[00041] Fin assembly 320 is configured to receive heat generated by LED 340
during operation from conductor 330, and is further configured to transfer the
heat by
convection to stack-effect airflow 312 flowing through fin assembly 320 and
duct 310.
In various embodiments, fin assembly 320 may be implemented with one type of
material or multiple types of materials. In one embodiment, conductor 330 and
fin
assembly 320 are substantially isothermal.
[00042] Exemplary fin 322, exemplary fin 324, and additional fins are shown
in
Fig. 3b arranged around a circumference of fin assembly 320. The plurality of
fins
including exemplary fin 322 and exemplary fin 324 is illustrative, and in
various
embodiments each of the plurality of fins has, for example, rectangular cross
sections, curved cross sections, aerodynamically-improved cross sections, or
other
cross sections. Although the plurality of fins are depicted as discrete fins
in Fig. 3b, in
other embodiments fin assembly 320 comprises an "overlapping" plurality of
fins
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having a more complex geometry, such as a grid geometry or a hexagonal
geometry.
[00043] Each of the plurality of fins of fin assembly 320 has a fin depth
shown in
Fig. 3b (e.g. the distance from an outer circumference of fin assembly 320 to
an
inner circumference of fin assembly 320). As also shown in Fig. 3b, each of
the
plurality of fins has a fin width, and is separated from adjacent fins by a
gap width
(e.g. a portion of a circumference of fin assembly 320). In one embodiment an
entire
circumference of fin assembly 320 comprises the assembly width. As shown in
Fig.
3a, each of the plurality of fins has a fin length (or "chord length") and a
fin depth.
Certain configurations of fin length, fin width, fin depth, and gap width
enable a heat
removal assembly of lighting apparatus 300 to achieve improved heat removal
performance according to the invention, in a manner corresponding to that
discussed
above with respect to lighting apparatus 100.
[00044] Notably, although Figs. 3a and 3b depict the fin depth of the
plurality of fins
as extending from an outer circumference to an inner circumference of fin
assembly
320, other embodiments may have a different configuration. For example, in
various
embodiments a fin may be attached to the outer circumference and extend only
partially inward toward the inner circumference, and in various other
embodiments, a
fin may be attached to the inner circumference and extend only partially
outward
toward the outer circumference. A third variety of embodiments includes two
groups
of such partially-extending fins respectively attached to either the inner or
outer
circumference.
[00045] Duct 310 is configured as a passage for stack-effect airflow 312,
which
flows through both fin assembly 320 and duct 310, and which carries heat away
from
fin assembly 320 by convection. In one embodiment, an outer surface of duct
310 is
implemented with a thermally insulating material (e.g., plastic) to prevent
thermal
interaction between stack-effect airflow 312 and the ambient environment. Duct
310
is configured with respect to fin assembly 320 to exploit a stack effect in a
manner
corresponding to that discussed above with respect to duct 110. Although stack-
effect airflow 312 is depicted as a line in Fig. 3a, it is understood that
stack-effect
airflow 312 is, in one embodiment, a flow of air through substantially the
volume
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unoccupied by the plurality of fins of fin assembly 320 and through
substantially the
volume between outer and inner circumferences of fin assembly 320 and duct
310.
Certain configurations of a duct length of duct 310 enable a heat removal
assembly
of lighting apparatus 300 to achieve improved heat removal performance
according
to the invention, in a manner corresponding to that discussed above with
respect to
lighting apparatus 100.
[00046] As depicted in Fig. 3a, the cross-sectional area of duct 310 through
which
stack-effect airflow 312 flows decreases with duct length, because the width
of duct
310 between inner and outer circumferences remains substantially constant
while
the diameter of duct 310 decreases. Accordingly, the velocity of stack-effect
airflow
312 in the narrowing passage increases while the local static pressure of
stack-effect
airflow 312 drops. This creates, in one embodiment, a favorable pressure
gradient
which keeps the boundary layers thin and prevents them from separating from a
surface of duct 310. The performance of stack-effect airflow 312 is thereby
enhanced.
[00047] Fig. 3c depicts a block diagram of lighting apparatus 301 according to
one
embodiment of the invention. Fig. 3c depicts a side view of lighting apparatus
301.
In the example of Fig. 3c, lighting apparatus 301 includes duct 311, fin
assembly
321, conductor 331, light emitting diode ("LED") 341, thermal storage system
351,
printed circuit board ("PCB") 361, light pipe 390, top reflector 392, and
bottom
reflector 394. Duct 311, fin assembly 321, conductor 331, and thermal storage
system 351 comprise a heat removal assembly of lighting apparatus 301. In some
embodiments of the invention, duct 311, fin assembly 321, conductor 331, LED
341,
and thermal storage system 351 substantially correspond to duct 310, fin
assembly
320, conductor 330, LED 340, and thermal storage system 350 of lighting
apparatus
300, except in variations noted below. Thus, as discussed above regarding
lighting
apparatus 300, in some embodiments of the invention a portion of the heat
generated by LED 341 during operation is transferred by conduction through
conductor 331 to fin assembly 321, and then transferred by convection to stack-
effect airflow 313 flowing through fin assembly 321 and duct 311, and another
portion of the heat is transferred by conduction through conductor 331 and fin
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assembly 321 to thermal storage system 351. In one embodiment of the
invention,
lighting apparatus 301 may omit thermal storage system 351.
[00048] As shown in Fig. 3c, LED 341 is disposed within lighting apparatus 301
and
is configured to shine up through light pipe 390. In contrast, as shown in
Fig. 3a,
LED 340 is disposed on a periphery of lighting apparatus 300 and is configured
in
one embodiment to shine down from lighting apparatus 300. Notably, in both
lighting
apparatus 300 and lighting apparatus 301, stack-effect airflow 312 and stack-
effect
airflow 313, respectively, are configured to flow upward. Thus, lighting
apparatus
300 is well suited, for example, for ceiling installations or other
installations where
light is to be directed substantially downward, and lighting apparatus 301 is
well
suited, for example, for floor installations or other installations where
light is to be
directed substantially upward.
[00049] Lighting apparatus 301 includes light pipe 390, top reflector 392, and
bottom reflector 394. Light pipe 390 is configured in various embodiments as,
for
example, a hollow guide, a guide with an inner reflective surface, a
transparent
plastic or glass guide, a fiber-optic guide, or another type of light guide.
Top reflector
392 is implemented as, for example, a translucent, decorative reflector
configured to
appear as a candle flame. In another embodiment, top reflector 392 is
implemented
as a lens or reflector for redirecting light from light pipe 390 in a
decorative manner
or in a utilitarian manner. Although depicted as having a partial diamond or
square
cross section in Fig. 3c, top reflector 392 is implemented, in other
embodiments, with
circular, rectangular, or other cross sections, for example. Bottom reflector
394 is
implemented with, for example, a mirrored surface which may be parabolic or
may
have another shape designed to maximize the amount of light going into light
pipe
390. Bottom reflector 394 may be positioned adjacent to LED 341, around LED
341,
or behind LED 341 with respect to light pipe 390. Light pipe 390 is configured
to
directly gather some or all of the light emitted by LED 341, and to guide the
gathered
light to top reflector 392. In one embodiment, some or all of the light that
is not
directly gathered by light pipe 390 is reflected from bottom reflector 394 and
redirected to light pipe 390. Light pipe 390 may thus indirectly gather some
of the
light emitted by LED 341 via bottom reflector 394. In some embodiments, top
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reflector 392 is omitted from lighting apparatus 301, such that light is
emitted directly
from light pipe 390.
[00050] As depicted in Figs. 3c, fin assembly 321 and duct 311 at least
partially
enclose a volume that is substantially occupied by other subassemblies of
lighting
apparatus 301. Fin assembly 321 and duct 311 may have a circular cross
sectional
shape similar to fin assembly 320 and duct 310 of lighting apparatus 300, or
may
have various other cross sectional shapes such as, for example, ellipsoidal,
triangular, rectangular, or yet other cross sectional shapes. Thermal storage
system
351, conductor 331, and light pipe 390 may have, in various embodiments,
similarly
varying cross sections. In one embodiment not depicted in Fig. 3c, fin
assembly 321
and duct 311 are configured to pass through an interior volume of either or
both of
thermal storage system 351 and conductor 331. In another embodiment not
depicted in Fig. 3c, light pipe 390 is not surrounded by thermal storage
system 351,
but is instead adjacent to thermal storage system 351 within a volume at least
partially enclosed by fin assembly 321 and duct 311. In another embodiment not
depicted in Fig. 3c, light pipe 390 surrounds either or both of thermal
storage system
351 and duct 311.
[00051] In one embodiment, LED 341 is coupled to mounting surface 333 of
conductor 331 in a manner similar to how LED 340 is coupled to mounting
surface
332 of conductor 330 of lighting apparatus 300. In another embodiment, LED 341
is
coupled to PCB 361 which is coupled to mounting surface 333 of conductor 331.
In
such an embodiment, PCB 361 may have a portion configured with low heat
resistance for heat transfer from LED 341 to conductor 331. Conductor 331 may
be
mounted at a center of fin assembly 321. In various embodiments, conductor 331
may be implemented with materials similar to those utilized for conductor 330
of
lighting apparatus 300. Conductor 331 may be implemented in a variety of
shapes
and sizes. In one embodiment of the invention, LED 341 is electrically coupled
to
PCB 361, which is configured in a manner similar to PCB 360 of lighting
apparatus
300. PCB 361 may be configured to fit within a circumference of thermal
storage
system 351. By so configuring PCB 361, lighting apparatus 301 advantageously
achieves, for example, a compact form that efficiently utilizes space.
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[00052] Fin assembly 321 is configured to receive heat generated by LED 341
during operation from conductor 331, and is further configured to transfer the
heat by
convection to stack-effect airflow 313 flowing through fin assembly 321 and
duct 311.
Fin assembly 321 may be implemented in a manner similar to fin assembly 320 of
lighting apparatus 300. Therefore, fin assembly 321 comprises, for example, a
plurality of fins arranged around a circumference of fin assembly 321. The
plurality
of fins may have, for example, rectangular cross sections, curved cross
sections,
aerodynamically-improved cross sections, or other cross sections, and may in
some
embodiments comprise an "overlapping" plurality of fins having a grid geometry
or a
hexagonal geometry, for example. Certain configurations of fin assembly 321
enable
a heat removal assembly of lighting apparatus 301 to achieve improved heat
removal performance according to the invention, in a manner corresponding to
that
discussed above with respect to lighting apparatus 300.
[00053] Duct 311 is configured as a passage for stack-effect airflow 313,
which
flows through both fin assembly 321 and duct 311, and which carries heat away
from
fin assembly 321 by convection. Duct 311 is configured with respect to fin
assembly
321 to exploit a stack effect in a manner corresponding to that discussed
above with
respect to duct 310. Although stack-effect airflow 313 is depicted as a line
in Fig. 3c,
it is understood that stack-effect airflow 313 is, in one embodiment, a flow
of air
through substantially the volume unoccupied by the plurality of fins of fin
assembly
321 and through substantially the volume between outer and inner
circumferences of
fin assembly 321 and duct 311. Certain configurations of a duct length of duct
311
enable a heat removal assembly of lighting apparatus 301 to achieve improved
heat
removal performance according to the invention, in a manner corresponding to
that
discussed above with respect to lighting apparatus 300. Although Fig. 3c
depicts the
cross-sectional area of duct 311 through which stack-effect airflow 313 flows
as
remaining substantially constant with duct length, in another embodiment the
cross-
sectional area of duct 311 decreases with duct length in a manner similar to
duct 310
of lighting apparatus 300.
[00054] Fig. 4 depicts installation 400, which includes lighting apparatus 300
installed in a recessed can in ceiling 480. In the example of Fig. 4, details
of lighting
apparatus 300 such as duct 310, fin assembly 320, conductor 330, LED 340,
thermal
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storage system 350, and PCB 360 are not depicted. Connector 370, not shown in
Figs. 3a and 3b, comprises a connector plug coupled to (e.g., screwed into) a
power
socket for providing power to lighting apparatus 300. In one embodiment,
connector
370 is coupled to PCB 360 via electrical wires disposed within or around
lighting
apparatus 300. Connector 370 may additionally comprise, in one embodiment, a
power supply configured to transform a voltage or current of the power socket
into a
voltage or current suitable for an LED driver circuit of PCB 360. In other
embodiments of the invention, instead of being installed in a recessed can in
ceiling
480, lighting apparatus 300 may be installed in, for example, a track-lighting
fixture, a
hanging fixture, a candelabra base, or another type of fixture. Although in
Fig. 4 a
portion of lighting apparatus 300 is depicted extending below a lowest surface
of
ceiling 480, in other embodiments lighting apparatus 300 may be level with a
lowest
surface of ceiling 480, or may be entirely above a lowest surface of ceiling
480 (e.g.,
completely enclosed within a recessed can of ceiling 480).
[00055] In the example of Fig. 4, stack-effect airflow 412 is shown. In some
embodiments of the invention, a portion of the heat generated by LED 340 of
lighting
apparatus 300 during operation is transferred by conduction to fin assembly
320, and
then transferred by convection to stack-effect airflow 412, in a manner
similar to
stack-effect airflow 312. Notably, in Fig. 4, stack-effect airflow 412 is
shown rising
inside lighting apparatus 300, and descending outside lighting apparatus 300
while
inside the recessed can of ceiling 480. Thus, in the example of Fig. 4, duct
310
inside lighting apparatus 300 also serves the unique function of separating an
incoming flow and an outgoing flow of stack-effect airflow 412. An outer
surface of
duct 310 may be implemented with a thermally insulating material (e.g.,
plastic) to
prevent thermal interaction between the incoming flow and the outgoing flow of
stack-effect airflow 412.
[00056] Duct 310 thus provides a clear and unobstructed path for air to rise,
to be
exhausted from lighting apparatus 300, to meet the upper surface of the
recessed
can and flow radially outward, and then to flow back down along the periphery
of the
recessed can and finally to exit out of the recessed can, where stack-effect
airflow
412 then flows radially outward along ceiling 480, away from lighting
apparatus 300.
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The unique configuration of installation 400, including lighting apparatus
300, thus
achieves improved heat removal performance according to the invention.
[00057] The words "herein," "above," "below," and words of similar import,
when
used in this application, shall refer to this application as a whole and not
to any
particular portions of this application. Where the context permits, words in
the above
Detailed Description using the singular or plural number may also include the
plural
or singular number respectively. The word "or," in reference to a list of two
or more
items, covers all of the following interpretations of the word: any of the
items in the
list, all of the items in the list, and any combination of the items in the
list.
[00058] The foregoing description of various embodiments of the claimed
subject
matter has been provided for the purposes of illustration and description. It
is not
intended to be exhaustive or to limit the claimed subject matter to the
precise forms
disclosed. Many modifications and variations will be apparent to the
practitioner
skilled in the art. Embodiments were chosen and described in order to best
describe
the principles of the invention and its practical application, thereby
enabling others
skilled in the relevant art to understand the claimed subject matter, the
various
embodiments and with various modifications that are suited to the particular
use
contemplated.
[00059] The teachings of the invention provided herein can be applied to other
systems, not necessarily the system described above. The elements and acts of
the
various embodiments described above can be combined to provide further
embodiments.
[00060] While the above description describes certain embodiments of the
invention, and describes the best mode contemplated, no matter how detailed
the
above appears in text, the invention can be practiced in many ways. Details of
the
system may vary considerably in its implementation details, while still being
encompassed by the invention disclosed herein. As noted above, particular
terminology used when describing certain features or aspects of the invention
should
not be taken to imply that the terminology is being redefined herein to be
restricted to
any specific characteristics, features, or aspects of the invention with which
that
terminology is associated. In general, the terms used in the following claims
should
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not be construed to limit the invention to the specific embodiments disclosed
in the
specification, unless the above Detailed Description section explicitly
defines such
terms. Accordingly, the actual scope of the invention encompasses not only the
disclosed embodiments, but also all equivalent ways of practicing or
implementing
the invention under the claims.
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